JP2008524787A - High-intensity discharge ballast - Google Patents

Abstract

A method and apparatus for supplying current to a load, the apparatus comprising a full or half-bridge switching circuit including at least one switching element adapted to supply power to the load when switched on; Means for switching the state of the switching element only when a substantially zero voltage is applied across the terminals of the switching element.
[Selection] Figure 5

Description

  The present invention relates to a power control apparatus that supplies power from an electric power company to a load according to desired voltage-current characteristics. In particular, but not exclusively, the present invention relates to a method and apparatus for supplying current to a high intensity discharge lamp via a lamp ballast with low power loss.

  There are many known situations when supplying power to a load. In such situations, the power supplied to the load must be accurately controlled to meet, but not exceed, the load threshold. An example of the load is a lamp, and one type is a high-intensity discharge lamp.

  High intensity discharge (HID) lamps have been commercially available for many years and consist of a sealed, usually double vessel in which a plasma discharge occurs. This discharge ionizes the gas that emits light at various wavelengths, depending on the composition of the gas in the discharge vessel.

  To obtain the longest service life, high efficiency energy conversion and safe operation requires tight control of the lamp operating conditions both at start-up and during operation. In the starting phase, an initial high voltage up to a few kilovolts must be applied across the lamp terminals in order to start the discharge. The power and current applied to the lamp must then be tightly controlled until the lamp reaches normal high temperature operating conditions. When the lamp operation changes from the starting mode to the normal operating stage, both the voltage across the lamp and the impedance of the lamp change significantly. Any ballast used to operate the lamp must take this into account.

Early passive ballasts consisted of an inductor in series with the power supply, roughly limiting the current entering the lamp, as shown in FIG. The impedance of inductor L1 is selected to be large compared to the impedance of the high efficiency lamp so that the change in lamp characteristics during operation and over the lifetime has a small effect on the lamp current. The capacitor C1 is necessary on the input side in order to bring the power factor (PF) close to 1 when the inductor delays the current by 90 degrees. In addition, the igniter circuit I1 is necessary to supply the high voltage and light the lamp first.
U.S. Pat. No. 4,725,762

  Due to the large size of L1, C1, and I1, the loss of L1, and the problem of maintaining good PF over the operating voltage range and lifetime of the ballast, the industry has solved with active electronic circuitry I moved to a plan. The latest electronic circuit solution can be found, for example, in Patent Document 1 by Otto Jagschitz. This is shown in FIG.

  Here, a complete bridge is used for two purposes, generating a high frequency resonant voltage to light the lamp and a low frequency controlled current during the operating state.

  During normal operation, when Q3 is on, Q4 is off, and vice versa, Q3 and Q4 are turned on and off at the appropriate low frequency. When Q3 is on, Q1 is always off, and similarly, when Q4 is on, Q2 is always off. If Q3 is on, Q2 is alternately turned on and off (pulse width modulated PWM) at a higher frequency than Q3 and Q4 to control the current through the load. Before Q2 turns on, all the current through L1 flows through D1, so Q2 needs to rectify this current before the cathode voltage at D2 drops to zero.

  The sequence in which Q2 is turned on is shown in the waveform of FIG. At time Т0, current is flowing through L1 and D1, and the total voltage appears across both terminals of Q2. At time Т1, Q2 begins to turn on, and at time Т2, the current of Q2 rises until the current of Q2 becomes equal to the current of L1. The current in Q2 continues to rise when D1 conducts in the opposite direction, it begins to recover and reaches a peak at Т3. By time Т4, D1 has fully recovered, its current has dropped to zero, and the voltage across Q2 has dropped to a low value. As can be seen from the waveform between time Т1 and Т3, current flows through Q2 and a full high voltage is applied across its terminals, thus consuming a large amount of energy when it is turned on. The peak current flowing during this time is the sum of the current of L1 and the peak reverse recovery current of D1.

  Referring to FIG. 4, at time Т6, Q2 starts to turn off and the current decreases. At the same time, the voltage between both terminals rises to the total power supply voltage, and the difference current between the current of L1 and the current of Q2 becomes D1. Flowing. Until Q2 is turned off at time Т7, the current of Q2 continues to decrease and the current of D1 continues to increase, and D1 conducts the entire current of L1. From the waveform, it can be seen that, between times Т6 and Т7, the full supply voltage is applied across both terminals of Q2, current flows through it, and thus a large amount of energy is consumed.

  A similar situation occurs when Q4 is on and Q1 is on and off with the diode current of D2. This switching method is called hard switching.

  The bridge is powered from any of a number of well known electronic pfc stages that provide a suitable stable high voltage rail.

There are three main problems with the prior art that are insufficient.
1) Hard switching of a complete bridge switch causes an increase in power loss as described above.
2) Hard switching causes the occurrence of electromagnetic interference (EMI) that needs to be suppressed by passing through a filter in the ballast.
3) The lamp current ripple is significant due to the single stage filter formed by L1 and C1.

  It is an object of the present invention to alleviate at least some of the above problems.

  It is an object of an embodiment of the present invention to provide an apparatus in the form of a circuit that controls the current applied to a load so that the load current meets a required threshold but does not exceed a predetermined threshold.

  It is an object of an embodiment of the present invention to provide a lamp ballast and a method for operating a lamp ballast in which the switching state of the switching element is switched only when zero or a minimum voltage is applied across both terminals of the switching element. It is. Thereby, the power loss is considerably reduced.

According to the first aspect of the present invention,
A full / half-bridge switching circuit including at least one switching element that supplies power to the load when switched on;
There is provided a power control apparatus for supplying current to a load, comprising means for switching the state of the switching element only when a substantially zero voltage is applied across the terminals of the switching element.

According to a second aspect of the invention,
Supplying a low-frequency controlled current to the load via a power controller including a full / half-bridge switching circuit in a normal operating mode;
A method of supplying current to a load is provided that includes switching a state of at least one switching element of the full / half-bridge switching circuit only when a substantially zero voltage is applied to the switching element.

  Embodiments of the present invention have the advantage that the switching elements of the lamp stabilization circuit are switched only when in a zero voltage state so that power consumption is reduced compared to prior art ballasts.

  Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

  The present invention retains the resonant lighting function for one full-bridge power conversion stage, reduces power loss, lamp ripple current, EMI, and improves efficiency while reducing the function of the current source to zero voltage switching ( ZVS).

  Although specific embodiments will be described with respect to lamp ballasts, embodiments of the present invention are widely applicable to power control used for various types of loads.

  Switches Q1-4 are shown as bipolar devices, but may be MOSFETs or other types of electronic switches. Diode D1 and capacitor C3 are part of switch Q1 or are separate. If C3 is part of the switching element, it is increased by the additional capacitance in parallel. The same applies to Q2, D2, C4, and Q3, Q4, and D3, D4.

  Referring to FIG. 5, during normal operation, Q3 and Q4 are turned on alternately at low frequencies. When Q3 is on, Q4 is off and vice versa. When Q3 is turned on, Q2 is turned on and off by pulse width modulation (PWM) using ZVS so as to keep the lamp current substantially constant. Q1 is turned off all the time that Q3 is on in this mode. The value of C2 is set so that the voltage of C2 does not change substantially during the time it takes for Q2 to turn on or off. The ZVS action will be described next with reference to the waveforms in FIGS.

  If Q2 is off, assume that at time Т0 in FIG. 6, Q3 and Q2 are on and the currents in Q2 and L2 have already increased. When it reaches the set value determined by the controller, Q2 is turned off at time Т1, and the voltage across Q2 begins to rise as the current in L2 charges the combined capacitance of C3 and C4. . The combined value of C3 and C4 limits the rate of increase of the voltage between both terminals of Q2. When the voltage reaches the power rail, D1 conducts. So L2 discharges its stored energy to C2, and the current flows through D1 until the current in L2 reaches zero (at which point D1 stops conducting).

  Referring to FIG. 7, the current of L2 reverses at time Т3 when D1 recovers, which forms a resonant ring with the coupling capacitance of C3 and C4, and the voltage across Q2 becomes zero at time Т4 when D2 conducts. Until it reaches, the voltage between both terminals of Q2 decreases. The controller then switches Q2 back on and the cycle repeats as long as Q3 is on.

  When Q3 is turned off and Q4 is turned on, Q1 is turned on and off in the same way as Q2, and Q2 is turned off all the time that Q4 is on. In this way, Q1 and Q2 are turned on and off, and the voltage between their terminals is approximately zero, thus minimizing switching losses. The rate at which the voltage across the switch changes is determined by C3, C4, and L2. Therefore, EMI or power loss can be optimized by changing these values.

  The circuit of FIG. 5 has an additional LC filter stage relative to the prior art, thus reducing lamp current ripple and reducing the possibility of acoustic arc resonance due to excessive current ripple.

  When the lamp is started and lit, Q1 and Q2 are driven alternately at high frequency to resonate L1 / C1 and generate the required high voltage across both terminals of the lamp to light it.

  Alternatively, Q3 and Q4 alone or in conjunction with Q1 and Q2 are driven at high frequency to resonate L1 / C1 and generate a high voltage to start the lamp.

  After the start of the lamp discharge, the operations of Q1 and Q2 proceed to the normal operation state described above to control the lamp current.

  As described above, the embodiment of the present invention has been described. According to this, regardless of whether the switch is on or off, the state is determined when the voltage between both terminals of the switching element is almost zero or considerably reduced. Only changes. In this way, the power consumed by the device is controlled.

  The embodiments of the present invention described above are exemplary only, and modifications may be made without departing from the scope of the invention. In particular, embodiments of the present invention can be applied with a half-bridge configuration.

1 shows a ballast in the prior art. Figure 2 shows another prior art ballast. Figure 3 shows the response of a part of a prior art circuit. Figure 3 shows the response of a part of a prior art circuit. 2 shows a lamp ballast according to an embodiment of the present invention. The timing and development of other parameters are shown. Fig. 6 shows the development of some parameters of the circuit of Fig. 5;

Explanation of symbols

C1-C4 capacitor D1-D4 diode I1 igniter circuit L1, L2 inductor Q1-Q4 transistor Т0-Т7 time

Claims (25)

A power control device for supplying current to a load,
A full / half-bridge switching circuit including at least one switching element that supplies power to the load when switched on;
Means for switching the state of the switching element only when a substantially zero voltage is applied across the terminals of the switching element.   The power controller of claim 1, wherein the power controller comprises a lamp ballast, the load comprises a lamp, and the full / half bridge switching circuit comprises a full bridge switching circuit.   The full bridge switching circuit comprises two pairs of diagonally opposed switching elements, each pair of first switching elements comprising at least one switching element, and when the remaining switching elements of the pair are on, the on-off The power control device according to claim 2, wherein the power control device is configured to remain off when the remaining switching elements are off.   The power control apparatus according to claim 3, wherein the two remaining switching elements are connected in series between a high power source and a low power source.   The power control device according to claim 4, wherein the lamp is connected to a connection point between the remaining switching elements via the first lamp terminal.   The power control apparatus according to claim 3, wherein the two first switching elements are connected in series between a high power source and a low power source.   The power control device according to claim 6, wherein a connection point between the two first switching elements is connected to the second lamp terminal via the first and second inductive elements.   The power control device according to claim 7, further comprising a capacitor connected between a connection point between the first inductive element and the second inductive element and the low power source.   In order to provide a resonant circuit with a first inductive element connected to the second lamp terminal to be connected in parallel with the lamp between the first lamp terminal and the second lamp terminal and to light the lamp during the start mode. The power control device according to any one of claims 2 to 8, further comprising a capacitor disposed on the surface.   The power control device according to claim 3, further comprising a capacitor element arranged in parallel with each first switching element.   The power control device according to claim 10, wherein each first switching element includes a MOSFET, and a capacitor element includes a parasitic capacitance of the MOSFET.   The power control apparatus according to claim 11, further comprising another capacitor connected in parallel with the parasitic capacitance of the MOSFET.   The power control device according to claim 10, wherein each first switching element includes a bipolar device, and the capacitor element includes an individual capacitor connected in parallel with the first switching element.   The power control apparatus according to claim 3, further comprising a diode element in parallel with each of the first switching elements.   The power control apparatus according to claim 14, wherein the first switching element includes a MOSFET, and the diode element includes a parasitic diode of the MOSFET.   The power control device according to claim 15, further comprising another diode element connected in parallel with the parasitic diode of the MOSFET.   The power control apparatus according to claim 14, wherein the first switching element includes a bipolar device, and the diode element includes an individual diode connected in parallel with each of the first switching elements.   First and second diodes are connected in series between a high power source and a low power source, and a connection point between the first diode and the second diode is a first inductive element and a second inductive element. The power control apparatus according to claim 7, wherein the power control apparatus is connected to a connection point between the elements. A method of supplying current to a load,
Supplying a low-frequency controlled current to the load via a power controller including a full / half-bridge switching circuit in a normal operating mode;
Switching the state of at least one switching element of the full / half-bridge switching circuit only when a substantially zero voltage is applied to the switching element.   20. The method of claim 19, wherein the load comprises a lamp, the full / half bridge switching circuit comprises a full bridge switching circuit, and the power controller comprises a lamp ballast. Further comprising providing a control signal to two pairs of opposing diagonal switching elements of the full bridge switching circuit to selectively turn the switching elements on and off, thereby
21. The method of claim 20, wherein each pair of first switching elements is switched on by a zero voltage switching sequence only when the remaining switching elements of the pair are on. Determining when the voltage at the connection point between the two first switching elements reaches a predetermined threshold voltage;
The method further comprises turning on one of the first switching elements when the threshold voltage is reached, wherein the first switching elements are connected in series in a full bridge switching circuit. The method described in 1.   21. A method according to any of claims 18 to 20, further comprising the step of lighting the lamp by a resonant circuit during start-up mode.   An apparatus constructed and arranged as described with reference to FIGS. 5-7 of the accompanying drawings.   8. The method described with reference to FIGS.

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